Restoration of voltage-dependent antibrain antibody-inhibited calcium current by cyclic adenosine monophosphate

A dual-microelectrode voltage clamp technique was used for recording voltage-dependent calcium current (I_ca) in unidentified neurons isolated fromHelix pomatia. Neither intracellular injection of cyclic adenosine monophosphate (cAMP; 10 nA, 5 min) nor intracellular application of dibutyril-cAMP (dcAMP; 1 mM, 10–20 min) induced a change in normal I_ca or produce a reversible 10–20% reduction in amplitude. Adding S-100 protein fraction antibodies to the external medium led to the onset of calcium-dependent inactivation of I_ca, bringing amplitude of I_ca down to 15±12% of its initial level. Either cAMP or dcAMP then restored inhibited I_ca to 50±11% of its original level. It was found that the effects of cAMP on I_ca of intact neurons depend on level of cytoplasmic Ca²⁺.Institute for Brain Research, All-Union Center for Mental Health Research, Academy of Medical Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 21, No. 2, pp. 247–252, March–April, 1989.     

Blood genetic marker studies of a sheep-goat hybrid and its back-cross offspring

Summary. Blood samples from a female sheep-goat hybrid and its back-cross male offspring were tested for electrophoretic variants of plasma albumin, transferrin and esterase, and of red cell carbonic anhydrase, nucleoside phosphorylase, NADH-diaphorase, 'X'-protein, superoxide dismutase, malic enzyme and haemoglobin. Red cells were also tested for blood group antigens. Both animals showed variants that could not be attributed to either sheep or goat alone, thus confirming previous chromosomal data that the female was a genuine sheep-goat hybrid.     

The effects of p-mercuribenzenesulfonate on purified spectrin and actin

The compound p-mercuribenzenefulfonate was found to affect the self-association behavior of both spectrin and actin. The reagent brings about the depolymerization of F-actin, as judged from the decrease in the fluorescence of an attached pyrene label, with a second-order rate constant an order of magnitude less than that for the disruption of isolated erythrocyte cytoskeletons. Therefore, it is unlikely that the depolymerization of actin is the rate-determining step in the mercurial-dependent disruption of the erythrocyte cytoskeleton. Low reagent concentrations caused an initial rapid dissociation of spectrin tetramers at a rate comparable with that of cytoskeleton disruption. Prolonged incubation, or higher reagent concentrations, resulted in subsequent aggregation of spectrin. The reagent also prevented the interaction between spectrin and actin, presumably through its depolymerization of actin and its effects on spectrin. The early event in the disruption of isolated erythrocyte cytoskeletons by p-mercuribenzenesulfonate thus appears to be the dissociation of spectrin oligomers. Subsequent depolymerization of actin brought about by the reagent then results in total disruption of the cytoskeleton.     

Polyproline binding is an essential function of human profilin in yeast.

Structural analysis of human profilin has revealed two tryptophan residues, W3 and W31, which interact with polyproline. The codons for these residues were mutated to encode phenylalanine and the mutant proteins overexpressed in Eschericia coli. The isolated proteins were diminished in their ability to bind polyproline, whereas phosphatidylinositol 4,5-bisphosphate (PIP2) binding remained unchanged. In many strains of Saccharomyces cerevisiae, disruption of the gene encoding profilin, PFY1, is lethal. It was found that expression of the gene for human profilin is capable of suppressing this lethality. The polyproline-binding mutant alleles of the human gene were cloned into various yeast expression vectors. Each of the mutant genes resulted in suppression of the lethality of pfy1Delta. It was observed that the mutant protein expression levels paralleled the growth rates of the strains. The severity of various morphological abnormalities of the strains was also attenuated with increased protein levels, suggesting that profilin polyproline-binding mutations are deleterious to cell growth unless overexpressed. Both tryptophan mutations were combined to give a third mutant allele that was found both unable to bind polyproline and to suppress the lethality of a pfy1 deletion. Immunoprecipitation experiments suggested that the mutants were unaltered in their affinity for actin and PIP2. These data strongly suggest that polyproline binding is an essential function of profilin.